Apparatus for carrying out underwater wellhead operations

ABSTRACT

Apparatus for carrying out underwater operations between a wellhead on the ocean bottom and a vessel floating on the water surface wherein the vessel is subject to wave motion. Interconnection means are suspended from the floating vessel adapted to operatively engage the wellhead to thereby provide fluid communication between the vessel and the wellhead. Hydropneumatically controlled wave motion cancelling means operatively engage the interconnection means to compensate for any wave motions acting on the vessel and thereby maintain the interconnection means in operative position.

United States Patent [191 Peterman et al.

[54] APPARATUS FOR CARRYING OUT UNDERWATER WELLHEAD OPERATIONSInventors: Charles P. Peterman, Houston, Tex.;

Glenn D. Johnson, Downey, Calif.; 7 William H. Petersen, Metairie, La

Assignee: Shell Oil Company, New York, N.Y.

Filed: Apr. 28, 1971 Appl. No.: 138,028

US. Cl 166/.5, 175/27, 175/5 Int. Cl. E2lc 19/00 References Cited UNITEDSTATES PATENTS 1/1971 Henderson 175/27 X 9/1965 Parks 175/27 X 2/1968Bohlmann 175/27 X Field of Search 175/5, 27; 166/.5

[ June 19, 1973 3,421,581 l/1969 Van Geijn 17515 X PrimaryExaminer-Marvin A. Champion Assistant Examiner-Richard E. FavreauAttorney-Harold L. Denkler and Theodore E. Bieber [57] ABSTRACTApparatus for carrying out underwater operations between a wellhead onthe ocean bottom and a vessel floating on the water surface wherein thevessel is sub ject to wave motion. Interconnection means are suspendedfrom the floating vessel adapted to operatively engage the wellhead tothereby provide fluid communication between the vessel and the wellhead.Hydropneumatically controlled wave motion cancelling means operativelyengage the interconnection means to compensate for any wave motionsacting on the vessel and thereby maintain the interconnection means inoperative position.

8 Claims, 5 Drawing Figures Pmmw Jmn ems smur FlG 1 INVENTORS. GLENN DJOHNSON CHARLES P. PETERMAN WILLIAM H. PETERSEN ATTORNEY PAIENIED J11!"9975 FIG 3 ENTO NSON RS TERMAN TERSEN lNv GLENN D. JOH CHARLES P. PEWILLIAM H. PE

ATTORNEY APPARATUS FOR CARRYING OUT UNDERWATER WELLHEAD OPERATIONSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to apparatus for carrying out operations, such as, for example,drilling, completion and production operations, with respect tounderwater wellheads from a cloating vessel. More particularly, theinvention relates to apparatus for compensating for wave motion which,acting on the vessel, is normally transmitted to interconnecting meansbetween the vessel and the underwater wellhead.

2. Description of the Prior Art In an attempt to locate new oil fields,an increasing amount of well-drilling has been conducted at offshorelocations, such as, for example, off the coast of California, Louisianaand Texas. As a general rule, the strings of casing in a well, togetherwith the tubing strings or string, extend to a point above the surfaceof the water where they are closed in the conventional manner that isused with respect to on-shore wells, with a conventional wellheadassembly being attached to the top of the casing. Such arrangementsconstitute a hazard to navigation, and recently methods and apparatushave been developed for drilling, completing and performing maintenanceoperations on wells wherein both the well casing head and subsequentlythe wellhead assembly and casing closure device are located underwaterat depths sufficient to allow ships to pass over them.

In the case of these latter underwater installations, some means must beprovided to carry out the various required operations with respect tothe underwater well and the wellhead assembly associated therewith. Thisproblem becomes especially difficult when the underwater well site is atsuch a distance below the surface of the ocean or other body of water soas to preclude the use of human divers. Accordingly, a wide variety ofspecial tools and components have been devised and utilized to remotelycarry out the desired underwater operations from vessels floating on thesurface of the water over a well site. These tools and components arelowered from the vessel to the location of the well by any one of avariety of methods, well known in the art, such as by means of pipestrings and/or guidelines extending downwardly from the floating vessel.

In the event pipe strings or their equivalent are used to carry outthese operations, some means must be employed to prevent buckling and/orbreakage thereof of equipment depending therefrom due to the riseandfall of the vessel on the surface of the water and a consequentialvariation in the distance between the vessel and the underwaterinstallation. Those familiar with the art have accordingly long sincerecognized the need for wave cancelling apparatus to compensate formovement of the floating vessel with respect to the underwater well. Asa consequence, various devices for accomplishing this end have beendeveloped, but such devices have been characterized by their complexityand have been prone to mechanical failure. In addition, prior artdevices of this type have normally been of such specialized constructionas to preclude their use on the wide variety of styles and types ofdrilling or service vessels without extensive alteration ormodification.

SUMMARY OF THE INVENTION It is thereforea primary object of the presentinven tion to provide apparatus whereby operations may be carried outwith respect to an underwater wellhead from a floating vessel.

It is a further object of the present invention to provide apparatus forperforming operations with respect to an underwater wellhead, suchapparatus including means for compensating for wave motion acting on afloating vessel which is normally transmitted to pipes or otherinterconnecting means between the vessel and the wellhead.

It is a still further object of the present invention to provide wavecompensation apparatus that is simple in construction and operation andis readily adaptable for use with a wide variety of drilling or servicevessels without alteration or modification and is a compatiblesupplement to commonly used wellhead equipment.

These and other objects are preferably accomplished by suspendinginterconnection means from a vessel floating on a water surface subjectto wave motion, the interconnection means being adapted to operativelyengage a wellhead on the ocean floor to thereby provide fluidcommunication between the vessel and the wellhead. Hydro-pneumaticallycontrolled wave motion cancelling means operatively engage theinterconnection means to compensate for any wave motions acting on thevessel and thereby maintain the interconnection means in operativeposition.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic elevationalview illustrating apparatus according to the present invention utilizedwith a conductor pipe depending from a floating vessel and operativelyassociated with .an underwater wellhead;

FIG. 2 is an enlarged side view in partial crosssection illustrating thewave arrester assembly according to the present invention; 7

FIG. 3 is an enlarged view taken along the line 33 in FIG. 2;

FIG. 4 is a schematic presentation of the hydropneumatic controlassembly utilized in the present invention; and 3 FIG. 5 is a detailedview of a of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, a floating vessel or platform is generally represented bynumeral 11. The vessel or platform 11 is of any suitable type,preferably one, as illustrated, floating at: the surface 10 of a body ofwater I2 and substantially fixedly positioned over a preselectedlocation on the ocean floor or sea bed 13 by suitable vessel-positioningmeans or by being anchored to the ocean floor by suitable anchors (notshown) connected to the anchor lines 14 and 15. Equipment of this typemay be used when carrying out operations with respect to underwaterwells, in water depths varying from about 100 to about 1,500 feet ormore. Vessel Ill is equipped with conventional drilling portion of theapparatus or workover equipment, such as a derrick (not shown) as wellas other auxiliary equipment, such as a conventional hoist systemincluding traveling block 16 and pipe elevator 17 depending therefrom.Mounted on work floor 18 of vessel 11 is a conventional rotary ma chine19 which is positioned over a well or slot 20 which extends verticallythrough the vessel 11 in a conventional manner. When using the equipmentof the present invention, the slot of the vessel 11 may be centrallylocated or extend in from one edge. However, drilling operations may becarried out over the side of the vessel or platform 11 without the useof a well or slot, as from a portion of the work floor 18 which may becantilevered out over one end of vessel 11.

Depending from vessel 11 is at least one pipe string 22 which cooperatesat its lowermost end with an underwater wellhead structure 23 which isaffixed to ocean floor 13 in the usual manner. Since a wide variety ofunderwater wellhead structure designs may be utilized in conjunctionwith the present invention and since such devices are well-known in theart, underwater wellhead structure 23 and its associated well bore 24have been illustrated only in a somewhat schematic fashion. It should,of course, be understood that in the event a producing well is havingoperations carried out with respect thereto, a production wellheadassembly permitting such operations would be the type of underwaterwellhead structure utilized. One underwater wellhead assembly suitablefor this purpose is disclosed in a U. S. Pat. No. 3,067,734. Of course,the apparatus according to the present invention may also be utilized inthe performance of certain well drilling operations conducted from afloating vessel, such as fishing jobs, landing pipe, setting packers,connecting flow lines, etc. In this latter situation, wellhead structure23 would be a drilling assembly, which may be of any known t e.

i ipe string 22 is supported by the wave arrester assembly (indicatedgenerally by numeral 25) in a manner that will be described in greaterdetail below. Wave arrester assembly 25, on the other hand, is supportedby floating vessel or platform 11' and extends through slot 20 of thevessel in the manner illustrated. More specifically, wave arresterassembly 25 extends through rotary machine 19 and is prevented fromfalling therethrough by means of any suitable device, as, for example,by a spider member 26 which is mounted on top of the rotary machine 19.Spider member 26 includes a lower base member 27 and a plurality of arms28 which are swivel-mounted on the base member and adapted to move tothe positions illustrated in FIG. 1 to cooperate with the wave arresterassembly 25 in a manner that will be described in greater detail below.Rather than using a spider for this purpose, any equivalent mechanism,such as slips, may be used for this purpose. Also disposed on boardvessel 11 is hydro-pneumatic control unit indicated generally byreference numeral 30. Hydro-pneumatic control unit 30 cooperates withwave arrester assembly 25 through control hose 31 in a manner to-bedescribed below. Control hose 31 may include suitable conduits (notshown) in fluid communication between unit 30 and assembly 25 all in themanner to be discussed further hereinbelow with particular regard toFIG. 4.

Referring now to FIG. 2, the wave arrester assembly 25, according to thepresent invention, is shown in detail. The wave arrester assembly 25includes a cylindrical body element 33'having an outer shell 34 and aninner shell 35 which is concentrically disposed with respect thereto.Although, in relatively short or normal stroke assemblies, these shellsare single lengths of suitable size pipe, in long stroke assemblies theymay include several sections that are joined together as by means of acoupling 36, the latter element being circumferentially welded to theshells 34 and 35 as shown. This construction not only serves to connectthe shell sections in an end-to-end manner, but, in addition, assists inmaintaining the concentric relationship between the inner and outershells at fixed intervals. Attached to the lowermost sections of outershell 34 and inner shell 35 as by means of welding is a skirt member 37.Skirt member 37 defines a downwardlyand outwardlyflared opening 38 withthe inner wall of the skirt member 37 defining the opening 38 serving asa guide for tool-joints and the like as they enter the lower end of thewave arrester assembly 25. Skirt member 37 includes an upwardly facingflange portion 39 of a diameter sufficient to accommodate tapped holes40 for receiving downwardly extending piston rods 41 as will bedescribed hereinbelow.

The upper end 42 of body element 33 forms a slip bowl 43 in the shape ofan upwardly and outwardly truncated conical bore 44 of a size anddimension sufficient to receive rotary slips 45 (FIG. 1) for the purposeof supporting the pipe string 22 from the wave arrester assembly 25. Ascan be seen in FIG. 5, slips 45 are preferably a removable, hingedassembly which land on surface 43 to wedge and grip pipe string 22. Slipbowl 43 (FIG. 2) further includes an outwardly extending flange 46, theupper face of which provides a seating surface 47 for supporting fromassembly 25 a travelling work platform 48 or the like (also shown indotted lines in FIG. 1), if desired. The lower face of flange 46includes a seating surface 48a for supporting wave arrester assembly 25from vessel 11 when the assembly 25 is being inactively employed as awave cancelling apparatus. Work platform 48 includes an L-shaped flange49 for bolting platform 48 to bowl flange 46 through a nut 50 and bolt50a or the like.

A plurality of hydraulic cylinders 51 are preferably circumferentiallyspaced about body element 33 and are in axial relationship thereto.These cylinders 51 are preferably even in number and arranged withone-half of the cylinders 51 (i.e., cylinders 51a as shown in FIGS. 2and 3) having their piston rods 52 disposed in an upwardly directedposition and the other half of the cylinders 51 (i.e., cylinders 51b asshown in FIG. 3) being situated in inter-adjacent relationship with thelatter piston rods 53 (FIG. 2) arranged in a downwardly directedposition. The downwardly directed piston rods 53 are threaded in tappedholes 40 of skirt member 37 and fastened thereto through means of jamnuts 54.

In order to retain cylinders 51 in fixed relationship, upper end plate55 and lower end plate 56 (plate 55 also being shown in FIG. 3) slidablyencompass body element 33 as can best be seen in FIG. 3. Plates 55 and56 are attached to each other by means of tie rods 57 or the like, rods57 being intermittently secured to end plates 55 and 56 by nuts 58 andjam nuts 59. Aperture means 60 (FIG. 3), formed in end plates 55 and 56,are coaxial with cylinders 51 andare substantially smaller in diameterthan the outside diameter of cylinders 51, yet large enough to allowfree movement of piston rods 52 and 53 passing therethrough (see alsoFIG. 4). Aperture means 60 are preferably counterbored (FIG. 4) toregister depth on the cylinder side of the end plates 55 and 56 so as toreceive the end portions of the cylinders 51 when in assembly.

A bushing 61 is slidably mounted on body element 33 and disposed belowslip bowl 43 and above the hydraulic cylinders 51. Tapped holes 62,corresponding to the '(FIG. 1). Thus assembled, the bushing 61 issupported from vessel 11 through spider member 26 which bushing 61 inturn supports the wave arrestor assembly 25 by shoulder engagement ofabutment 67 and seating surface 48. Such support is accomplished only aslong as there is insufficient pressure in the piston rods 52 and 53 tosupport the combined weight of the load of suspended pipe string 22, thewave arrestor assembly 25, etc, other than the weight of the bushing 61and upper piston rods 52. By application of cylinder pressure sufficientto overcome this weight combination, the wave arrestor assembly 25 andits supported pipe string 22 move upwardly thus transferring the loadfrom the bushing 61 to the hydraulic cylinders 51.

in operation, when it is desired that wave arrestor assembly 25 functionas a wave cancellation means, sufficient fluid volume is applied tocylinders 51 to elevate assembly 25 to a point where, in operation,shoulder engagement of abutment 67 and seating surface 48 does not takeplace. This operation requires hydraulic pressure in the system ofsufficient magnitude to overcome the weight loads of the pipe string 22,assembly 25, etc. The volume of fluid in cylinders 51 must bedelicatelymaintained so that vertical motion of vessel 11 is nottranslated into motion on pipe string 22. This may be accomplished byproviding a gas balancing cushion to the hydraulic fluid inhydro-pneumatic control unit 30 as will be discussed furtherhereinbelow.

Referring now to FIG. 4, unit 30 and wave arrestor assembly 25 are shownschematically. The piston rod or pressure side of the hydraulic cylindercontrol hose 31 interconnecting the wave arrestor assembly 25 to unit 30is essentially connected to the hydraulic fluid side 73 of the surgecylinder 68 of unit 30. This closed cylinder 68 is provided with apiston 69 having an attached rod 70 passing through packing gland 71 atthe hydraulic fluid side 73 of cylinder 68. Piston 69 also includes arod marker 72 at its outer end for reasons to be discussed furtherhereinbelow. A compressible gas, such as air, is contained in cylinder68 in the opposing side 74 of the piston 69.

In the operable position of the wave arrestor assem- My 25, the pressureair side 74 of surge cylinder 68 is adjusted to balance the weight ofpipe string 22 with the arrestor assembly 25 positioned at the desiredelevation with respect to vessel 11. A surge chamber 75,

having an air or the like chamber 76 therein, supplements thedisplacement of air or the like chamber 68 to reduce the air orgaspress'ure differential as the noncompressible hydraulic fluid actingon the piston 69 causes piston 69 to stroke within cylinder 68. A highpressure reserve tank 77, having an air or the like chamber 78 therein,and an air or gas compressor 79 coupled thereto, is provided forcharging and maintaining the air (or gas) pressure within the surgechamber 75 and the air (or gas) side 74 of surge cylinder 68. A suitableair or gas compressor 79 is any compressor characterized by relativelylow volumetric displacement for adequate pressure requirements. Thereserve tank 77 acts as an immediate reserve to adjust pressure in thesurge portion of unit 30'.

Thus, as can be seen in FIG. 4, the pressure or piston rod side ofcylinders 51 are all in connected communication through suitableconduits 82 and 83, i.e., conduit 31 in FIG. 1, to the fluid side 73 ofsurge cylinder 68. In a preferred adjustment, the system is closed,i.e., charged with sufficient volume so that, with cylinders 51 fullyextended, the limit of discharge in the surge cylinder 68 is effected.When the displacement of cylinder 68 is set equal to that of cylinders51, the stroke limits in each are synchronized.

A hydraulic pump 84, together with a conventional accumulator 85, ispreferably coupled to conduit 83 as shown for initially charging thehydraulic portion of the system and to replenish the volume of thehydraulic fluid in the event of leakage. The fluid side of the systemalso includes a reservoir sump 86 for both supplying fluid to the systemand serving as a surge tank for the non-pressure side of cylinders 51.The operation of the remaining components of the system (i.e., unit 30and assembly 25) such as block valves 87 through 90, motor 97, three-waycontrol valve 91, three-way valve 92, relief valve 93, gauge 94, andvalve actuators 95 and 96, will become apparent from the followingdescription of operation of the system.

To Charge the Hydraulic System With the valves positioned as follows:

(89) open (90) closed (91) all ports blocked (88) open (92) surgechamber vented to atmosphere (87) closed First, wave arrestor assembly25 is extended to maximum stroke limit (the arrestor assembly 25 beingsupported from the bushing 61). Surge cylinder piston 69 is moved to thelimit of its stroke on the fluid side 73 of cylinder 68.

Second, motor 97 is actuated and pump 84 is started and valve 91 ispositioned to slowly allow fluid to enter the wave arrestor cylinders 51and the fluid side of the surge cylinder piston 69. Fluid pressure fromthe pump 84 causes the wave arrestor cylinders 51 to close and thepiston 69 of the surge cylinder 68 to be moved to the gas side 74 of thecylinder 68.

Third, valve 90, the highest point in the system, is opened and allgases purged from the fluid side of the surge cylinder 68.

Fourth, valve 90 is closed and surge piston 69 is moved to its maximumlimit of stroke towards the fluid side 73 of cylinder 68. This expelsall fluid from surge cylinder 68 into reservoir 86.

Fifth, wave arrestor assembly 25 is extended to maximum stroke limit.All fluid in the arrestor cylinders 51 is transferred to the fluid side73 of the surge cylinder" (89) open (90) closed (9l) surge cylinder opento wave arrestor assembly 25--pump port unlocked (88) closed (92) allports blocked (87) closed First, valve 88 is opened to equalize thepredetermined gas pressure between surge cylinder 68 and surge chamber75.

Second, valve 91 is opened to introduce high pressure fluid to the wavearrestor cylinders 51 from the reserve fluid accumulator 85. The aboveoperation causes the wave arrestor cylinders 51 to close. The

closing of the wave arrestor cylinders 51 to their desired position iscontinued, preferably at 100 percent stroke.

Third, with the cylinders 51 of the wave arrestor assembly 25approximately 100 percent closed and with piston 69 or surge cylinder 68at maximum limit of stroke on the fluid side 73 of cylinder 68, slips 45on pipe string 22 are placed at the upper end of arrestor assembly 25and elevator 17 is removed from pipe string 22 (as shown in FIG. 1). Theweight of pipe string 22 on wave arrestor assembly 25 causes wavearrestor assembly 25 and surge piston 69 to move to the mid-position oftheir respective strokes as gas in the gas side 74 of the cylinder 68 iscompressed to its predetermined volume. Both wave arrestor assembly 25and cylinder piston 69 are now in a condition to move freely toaccommodate for vertical vessel motion.

To adjust the Spacing of the Wave Arrestor Assembly (under constantload) To raise or lower a pipe riser supported by the wave arrestorassembly 35, such as would be necessary to connect or disconnect theriser from an ocean floor structure, valve 91 is manipulated to add orsubtract fluid from the cylinders 51. With constant axial load on thewave arrestor assembly 25, piston 69 remains in a fixed position as thecylinders 51 are opened or closed. To Adjust Axial Pull of the WaveArrestor Assembly With the wave arrestor assembly 25 dynamicallysupporting the upper end of a pipe riser and with the lower end fixed tothe ocean floor, it is possible to vary the axialpull applied to theriser by the wave arrestor assembly 25 by increasing or decreasing thegas pressure in the surge cylinder 68 and the surge chamber 75. This isreadily accomplished by manipulating valve 92 to admit high pressure gasto the accumulator 85 from reserve tank 77 or by venting the surgechamber 75 to atmosphere.

To Adjust the Spacing of the Surge Cylinder Piston With the wavearrestor assembly 25 supporting a riser that is connected to the oceanfloor, it may be necessary from time to time to reposition the surgepiston 69 to the midpoint of its stroke within the surge cylinder 68. Itis essential in order to maintain proper flow of fluid to the wavearrestor assembly 25 that the surge cylinder piston 69ibe confinedwithin its limit of travel in the surge cylinder 68.

Positioning of surge piston 69 may be accomplished by manipulating valve91 to add or subtract fluid from the surge cylinder 68 to the reservoirsump 86 causes the piston 69 to shift to the fluid side 73 of thecylinder 68. Alternatively, by moving valve 91 to add fluid to the surgecylinder 68, the piston 69 moves to the gas side 74 of the cylinder 68.

In addition, automatic positioning of the surge piston 69 may beaccomplished by use of travel indicating pawls 80 and 81 slidablymounted on the surge cylinder mount 98. The indicating pawls may be usedin coordiautomatically position valve 91 as required to keep piston 69in proper position.

In summary, apparatus has been described for carrying out underwateroperations between a wellhead on the ocean floor and a vessel floatingon the water surface wherein the vessel is subject to wave motion. Apipe string or other interconnecting means is provided between thevessel and the wellhead with the support for the interconnecting meansbeing provided by a wave arrester assembly. The interconnecting meansextends through the wave arrester assembly and is held in supportiveengagement therewith by means of slips. The portion of the wave arresterassembly which is interconnected to the interconnecting means is biasedin an upward direction and is relatively movable with respect to asupport and guide bushing. The support and guide bushing provide meanswhereby the wave arrester assembly may be supported from the vessel, asupon a conventional rotary table mounted on the vessel. The wavearrester assembly includes a plurality of piston-cylinder arrangementsinterconnected to the hydro-pneumatic control unit which are effectiveto maintain the wave arrester assembly in the desired operativecondition. The wave arrester assembly may be adapted to accommodate atravelling work platform to assist in the performance of the desiredoperations with respect to the underwater wellhead.

We claim as our invention: 30 1. Apparatus for carrying out underwateroperations between a wellhead on the ocean bottom and a vessel floatingon the water wherein said vessel is subject to wave motion, saidapparatus comprising:

interconnection means suspended from said floating vessel and adapted tooperatively engage said wellhead to thereby provide fluid communicationbetween said vessel and said wellhead; and hydropneumatically controlledwave motion canceling means adapted to compensate for any wave motionacting on said vessel, said interconnection means extending through saidwave motion canceling means and being operatively coupled to said wavemotion canceling means; and said wave motion canceling means in additionbeing releasably carried by said floating vessel and including adownwardly and outwardly flared opening at its lowermost end. 2.Apparatus for carrying out underwater operations between a wellhead onthe ocean bottom and a vessel 50 floating on the water wherein saidvessel is subject to wave motion, said apparatus comprising:

interconnection means suspended from said floating vessel adapted tooperatively engage said wellhead to thereby provide fluid communicationbetween said vessel and said wellhead; and hydropneumatically controlledwave motion canceling means operatively engaging said interconnectionmeans, said wave motion canceling means including a substantiallycylindrical body element and plurality of hydraulic cylinders slidablyand outwardly engaging said body element, at least some of saidcylinders having their piston rods disposed in an upwardly directedposition and at least some of said cylinders having their piston rodsdisposed in a downwardly directed position; the upper and lower ends ofall of said cylinders lying substantially in the same plane; and

upper and lower plate means abutting the upper and lower ends of all ofsaid cylinders, respectively, for retaining said cylinders therebetween,said plate means having apertures therein for passing all of said pistonrods slidably therethrough.

3. The apparatus of claim 2 including abushing member fastened to thefree ends of the upwardly directed piston rods, said bushing memberbeing slidably mounted on said cylindrical body element; and

the free ends of the downwardly directed piston rods being fixedlysecured to approximately the lowermost end of said body element.

4. The apparatus of claim 2 wherein said bushing member includesabutment means thereon adapted to releasably retain slip means connectedto said vessel to thereby releasably retain said wave motion cancellingmeans in fixed position with respect to said vessel.

5. The apparatus of claim 4 wherein said body element includes bushingmember limit means at its upper end adapted to be engaged by saidbushing member to limit the upper movement thereof with respect to saidbody element.

6. The apparatus of claim 5 wherein said hydropneumatically controlledwave motion cancelling means includes hydraulic fluid supply meanscoupled to said cylinders for selectively supplying sufficient hydraulicfluid thereto to selectively release and transfer the load to and fromsaid bushing member to said cylinders.

7. The apparatus of claim 6 wherein said hydropneumatically controlledwave motion cancelling means further includes hydraulic fluid supplycontrol means operatively engaging said hydraulic fluid supply means formaintaining sufficient hydraulic fluid under pressure in said cylindersso that vertical motion on said vessel is not translated into motion onsaid interconnecting means.

8. The apparatus of claim 7 wherein said hydraulic fluid supply controlmeans includes a surge cylinder having a compressible pressure gas sideand a noncompressible hydraulic fluid side, the pressure gas side beingadapted to be adjusted to balance the weight of the interconnectionmeans when the hydropneumatically controlled wave motion cancellingmeans is positioned at its desired elevation with respect to saidvessel.

1. Apparatus for carrying out underwater operations between a wellheadon the ocean bottom and a vessel floating on the water wherein saidvessel is subject to wave motion, said apparatus comprising:interconnection means suspended from said floating vessel and adapted tooperatively engage said wellhead to thereby provide fluid communicationbetween said vessel and said wellhead; and hydropneumatically controlledwave motion canceling means adapted to compensate for any wave motionacting on said vessel, said interconnection means extending through saidwave motion canceling means and being operatively coupled to said wavemotion canceling means; and said wave motion canceling means in additionbeing releasably carried by said floating vessel and including adownwardly and outwardly flared opening at its lowermost end. 2.Apparatus for carrying out underwater operations between a wellhead onthe ocean bottom and a vessel floating on the water wherein said vesselis subject to wave motion, said apparatus comprising: interconnectionmeans suspended from said floating vessel adapted to operatively engagesaid wellhead to thereby provide fluid communication between said vesseland said wellhead; and hydropneumatically controlled wave motioncanceling means operatively engaging said interconnection means, saidwave motion canceling means including a substantially cylindrical bodyelement and plurality of hydraulic cylinders slidably and outwardlyengaging said body element, at least some of said cylinders having theirpiston rods disposed in an upwardly directed position and at least someof said cylinders having their piston rods disposed in a downwardlydirected position; the upper and lower ends of all of said cylinderslying substantially in the same plane; and upper and lower plate meansabutting the upper and lower ends of all of said cylinders,respectively, for retaining said cylinders therebetween, said platemeans having apertures therein for passing all of said piston rodsslidably therethrough.
 3. The apparatus of claim 2 including a bushingmember fastened to the free ends of the upwardly directed piston rods,said bushing member being slidably mounted on said cylindrical bodyelement; and the free ends of the downwardly directed piston rods beingfixedly secured to approximately the lowermost end of said body element.4. The apparatus of claim 2 wherein said bushing member includesabutment means thereon adapted to releasably retain slip means connectedto said vessel to thereby releasably retain said wave motion cancellingmeans in fixed position with respect to said vessel.
 5. The apparatus ofclaim 4 wherein said body element includes bushing member limit means atits upper end adapted to be engaged by said bushing member to limit theupper movement thereof with respect to said body element.
 6. Theapparatus of claim 5 wherein said hydropneumatically controlled wavemotion cancelling means includes hydraulic fluid supply means coupled tosaid cylinders for selectively supplying sufficient hydraulic fluidthereto to selectively release and transfer the load to and from saidbushing member to said cylinders.
 7. The apparatus of claim 6 whereinsaid hydropneumatically controlled wave motion cancelling means furtherincludes hydraulic fluid supply control means operatively engaging saidhydraulic fluid supply means for maintaining sufficient hydraulic fluidunder pressure in said cylinders so that vertical motion on said vesselis not translated into motion on said interconnecting means.
 8. Theapparatus of claim 7 wherein said hydraulic fluid supply control meansincludes a surge cylinder having a compressible pressure gas side and anon-compressible hydraulic fluid side, the pressure gas side beingadapted to be adjusted to balance the weight of the interconnectionmeans when the hydropneumatically controlled wave motion cancellingmeans is positioned at its desired elevation with respect to saidvessel.